Optimization of thrust force in drilling of carbon-basalt hybrid composites through Taguchi and RSM

The main object of the present work is to obtain better quality holes during drilling operation. Carbon-Basalt hybrid composite is a better performing composite with lesser price. For the present work, the hybrid composite test specimen was prepared by hand layup method. General purpose polyester resin is used as the matrix material. During the manufacturing process, alternate layers of carbon and basalt are stacked to prepare the composite. The maintained weight fraction of the fiber is 50%. The thickness of the obtained composite specimen is 6 mm. Delamination is the major reason for the rejection of drilled composites. The magnitude of delamination is directly proportional to the thrust force generated during drilling. Hence in the present work, an attempt has been made to reduce the thrust force to minimize the damage by optimizing the machining variables using Taguchi and RSM methods. The experiments were designed by DOE method. Taguchi's 3 levels and 3 factors array was used to get the combination of parameters for each experiments. Totally 27 holes are drilled with different combinations of process parameters. The considered process parameters and their levels are: Drill diameter (6 mm, 8 mm & 10 mm), feed rate (50 mm/min, 75 mm/min & 100 mm/min) and spindle speed (750 rpm, 1000 rpm & 1250 rpm). Drilling process was carried out on a high precision CNC machine using HSS drill bits. The thrust force was measured by a Kistler dynamometer. Using ANOVA, the significant effect of considered parameters on the generated thrust force was also predicted. The result reveals that, the parameter feed rate has the most significant effect on thrust force, which is followed by the drill diameter. The least significant parameter is spindle speed. Both Taguchi and RSM methods suggest that, DD1, F1 and S3 combination parameters yields the lowest thrust value.